Sahih Bukhari, Chapter: Fasting

Allah's Apostle forbade Al-Wisal in fasting. So, one of the Muslims said to him, "But you practice Al-Wisal. O Allah's Apostle!" The Prophet replied, "Who amongst you is similar to me? I am given food and drink during my sleep by my Lord." So, when the people refused to stop Al-Wisal (fasting continuously), the Prophet fasted day and night continuously along with them for a day and then another day and then they saw the crescent moon (of the month of Shawwal). The Prophet said to them (angrily), "If It (the crescent) had not appeared, I would have made you fast for a longer period." That was as a punishment for them when they refused to stop (practising Al-Wisal).